The development of gas generating compositions capable of optimum performance as propellants in aerospace applications has presented significant challenges. Ideal compositions must be characterized by stability, low sensitivity and an exhaust output when combusted that achieves optimum ballistic properties while producing combustion products that are compatible with system components. Such ideal gas generating compositions, moreover, should optimally be formulated from readily available, cost effective, components. Available propellant composition components have proved to be effective gas generators; however, the cost of component availability, and system compatibility have been drawbacks. Additionally, some available propellant compositions have a Class 1.1 hazards rating, which limits their utility in aerospace and similar applications where highly sensitive compositions are not desirable. Most highly filled solid rocket propellants, moreover, have limited working lives, in part because of processing methods that produce higher than desired end of mix viscosities.
The prior art has proposed a number of propellant compositions useful as rocket fuels and the like. U.S. Pat. No. 5,053,086 to Henry et al., for example, discloses a liquid castable gas generant composition useful as a solid rocket propellant formed from a high nitrogen content solid and an energetic polymer. The high nitrogen content solid may be one of several disclosed tetrazole and bitetrazole compounds, and the energetic polymers are liquid curable rubbers, with several oxetane copolymers preferred. The Henry et al. composition is stated to produce higher burn rates, on the order of 0.23 to 0.66 in/sec at 1000 psia, and flame temperatures of 1901.degree. to 2291.degree. F.
In U.S. Pat. No. 3,898,112, Strecker et al. disclose a solid gas generating propellant that produces total pressure immediately when the guidance of a missile is dependent on instantaneous total pressurization. This composition incorporates 75 to 87% 5-aminotetrazole nitrate in a block copolymer binder, preferably styrene-butadiene-styrene or styrene-isoprene-styrene, with optional antioxidants and plasticizing agents. An exemplary formulation produces a burning rate of 0.420 in/sec at 1000 psi and 77.degree. F.
The propellant composition described in U.S. Pat. No. 3,354,172 by Takaes is composed of triamino-guanidinium 5-amino-tetrazolate, an oxidizer, and a binder. This composition, which is disclosed to be characterized by high stability and to have a large gas- forming capability, includes conventional oxidizers and a binder such as nitrocellulose and can include fuels such as aluminum, beryllium and boron.
U.S. Pat. No. 3,668,873 to Bauman discloses rocket propellant systems that provide thrust by employing a highly exothermic reaction of nitridable inorganic fuels and an oxidizing nitrogen source, such as 5-amino tetrazole.
Gawlick et al. in U.S. Pat. No. 3,707,411, discloses a solid propellant that includes a mixture of nitrocellulose and 5 to 80% by weight of a percussion-sensitive diazo, triazole or tetrazole derivative, such as 5-aminotetrazole. The brisance of the mixture can be varied by including explosive nitrated esters. This propellant is disclosed to be useful for annular caseless propellant cartridges, for example, stud driving tools, in which an explosive action is desired.
Gas generating compositions containing 5-amino-tetrazole and an oxidizer and a nitrogen gas-producing energetic compound, an oxidizer salt and a cellulose-based binder are disclosed, respectively, in U.S. Pat. No. 5,661,261 to Ramaswamy et al. and U.S. Pat. No. 5,125,684 to Cartwright. However, the compositions described in these patents are intended for use in automotive air bags and are formulated to respond to specific functional considerations that are distinctly different from those in aerospace and similar applications.
The prior art, therefore, has failed to disclose a family of gas generating compositions useful as propellants in aerospace applications that has a stable component formulation characterized by low sensitivity, a flame temperature less than 3050.degree. F., combustion exhaust products with optimum system compatibility, optimum ballistic properties and increased working life, and that can be formulated cost effectively from available components. The prior art has further failed to disclose a method for making a family of gas generating compositions that produces compositions with improved working lives and mechanical properties. A need exists for such a family of compositions and method for making them.